We report a high-speed phase-sensitive optical coherence reflectometer (OCR) with a stretched supercontinuum source.
Firstly, supercontinuum source has been generated by injecting an amplified fiber laser pulses into a highly nonlinear
optical fiber. The repetition rate and pulse duration of the generated supercontinuum source are 10 MHz and 30 ps
respectively. The supercontinuum pulses are stretched into 70 ns pulses with a dispersion-compensating fiber (DCF).
This pulse stretching technique enables us to measure the spectral information in the time domain. The relationship of
time-wavelength has been measured by modified time-of-flight method. We have built a phase-sensitive OCR with this
stretched pulse source and a two-dimensional (2D) scanning system. The displacement sensitivity of our proposed
system has been investigated. We have demonstrated high-speed 2D imaging capability and single-point dynamics
measurement performance of our proposed system.
Two-photon microscopy is a very attractive tool for the study of the three-dimensional (3D) and dynamic processes in
cells and tissues. One of the feasible constructions of two-photon microscopy is the combination a confocal laser
scanning microscope and a mode-locked Ti:sapphire laser. Even though this approach is the simplest and fastest
implementation, this system is highly cost-intensive and considerably difficult in modification. Many researcher
therefore decide to build a more cost-effective and flexible system with a self-developed software for operation and data
acquisition. We present a custom-built two-photon microscope based on a mode-locked Yb<sup>3+</sup> doped fiber laser and
demonstrate two-photon fluorescence imaging of biological specimens. The mode-locked fiber laser at 1060 nm delivers
320 fs laser pulses at a frequency of 36 MHz up to average power of 80 mW. The excitation at 1060 nm can be more
suitable in thick, turbid samples for 3D image construction as well as cell viability. The system can simply accomplish
confocal and two-photon mode by an additional optical coupler that allows conventional laser source to transfer to the
scanning head. The normal frame rate is 1 frames/s for 400 x 400 pixel images. The measured full width at half
maximum resolutions were about 0.44 μm laterally and 1.34 μm axially. A multi-color stained convallaria, rat basophilic
leukemia cells and a rat brain tissue were observed by two-photon fluorescence imaging in our system.
Confocal laser scanning microscopy (CLSM) has become the tool of choice for high-contrast fluorescence imaging in the
study of the three-dimensional and dynamic properties of biological system. However, the high cost and complexity of
commercial CLSMs urges many researchers to individually develop low cost and flexible confocal microscopy systems.
The high speed scanner is an influential factor in terms of cost and system complexity. Resonant galvo scanners at
several kHz have been commonly used in custom-built CLSMs. However, during the repeated illumination for live cell
imaging or 3D image formation, photobleaching and image distortion occurred at the edges of the scan field may be
more serious than the center due to an inherent property (e.g. sinusoidal angular velocity) of the scan mirror. Usually, no
data is acquired at the edges due to large image distortion but the excitation beam is still illuminated. Here, we present
the photobleaching property of CLSM with masked illumination, a simple and low cost method, to exclude the
unintended excitation illumination at the edges. The mask with a square hole in its center is disposed at the image plane
between the scan lens and the tube lens in order to decrease photobleaching and image distortion at the edges. The
excluded illumination section is used as the black level of the detected signals for a signal quantizing step. Finally, we
demonstrated the reduced photobleaching at the edges on a single layer of fluorescent beads and real-time image
acquisition without a standard composite video signal by using a frame grabber.
We report a scheme for controlling pulse width in a robust self-starting mode-locked ytterbium fiber laser using a
semiconductor saturable absorber mirror (SESAM). We demonstrate that the pulse width in a mode-locked laser made
of all-normal-dispersive fiber can be adjusted by changing ump power to the laser or by adjusting the axial position of
the SESAM with respect to a focusing beam. We have obtained optical pulse width of 7.4 ps and the adjustable range
was 2 ps without dispersion compensators in the all-normal-dispersive cavity and provides a high reliability of turn-key
operation. We have explained that the principle of position dependent pulse width change in a mode-locked laser with a
SESAM and verified with numerical simulations.
We constructed a passively mode-locked Er-doped fiber laser (PML-EDFL). It generates ~ 1.3 ps pulses at a repetition
rate of 12 MHz with an average output power of 0.7 mW. These pulses are amplified in a short Er-doped fiber amplifier
(EDFA) which is composed of low nonlinearity EDF. The average power of amplified pulse is about 15 mW. And its
pulse width is about 880 fs. An all-fiber supercontinuum (SC) is generated by putting the amplified fiber laser pulse at
the wavelength of 1. 56 &mgr;m into the highly nonlinear dispersion shifted fiber (HN-DSF) whose zero dispersion
wavelength is 1.537 &mgr;m and nonlinear coefficient is about 10.5/W/km at the input wavelength. The polarization state of
the generated SC spectra is well defined such that it can be properly controlled by the polarization controller. By using a
delayed pulsed method, we report an experimental study of the coherence of SC spectra generated through a HN-DSF.
In this paper, the strong dependence of the spectral coherence on the HN-DSF length is observed experimentally. And
optimal conditions for obtaining wide SC with high coherence are investigated in detail. We believed that our proposed
all-fiber laser based SC source with high coherence has many important applications in recently developed frequencydomain
measurement techniques such as optical coherence tomography (OCT), optical frequency domain imaging
(OFDI), optical frequency domain reflectometry (OFDR) and their instrumentation.
We report a wideband and almost flat spectrum supercontinuum (SC) generation by using a passive mode-locked Er-doped fiber laser (PML-EDFL) and a highly nonlinear dispersion shifted fiber (HN-DSF). The fiber laser pulses are characterized with a conventional second harmonic generation frequency resolved optical gating (SHG-FROG) method. The dependence of the SC spectral width on the HN-DSF length, the spectral stability of the generated SC spectrum, and conditions for obtaining smooth spectra without a fine structure are investigated experimentally. In this paper, wide spectrum covering 1100-1750 nm wavelength range is generated with only 8.5 cm long HN-DSF when laser is single pulse operation regime. In addition, the flat spectrum with ±1 dB uniformity was obtained at the wavelength region of 1130-1510 nm. And spectral stability is about ±0.2 dB at the uniformity wavelength region. We believe that our proposed all-fiber based SC source has many important applications in recently developed frequency-domain measurement techniques such as optical coherence tomography (OCT), Optical frequency domain imaging (OFDI), optical frequency domain reflectrometry (OFDR), and their instrumentation.